1. Field of the Invention
This invention relates to eyeglass cases having a cushioning lining and to the method of manufacture thereof. More specifically, the invention relates to such eyeglass cases in which a reinforced bar tear seal (BTS) is used to adhere the edges of the eyeglass case together.
2. Description of the Prior Art
The most common types of "open end" construction for eyeglass cases involve a sewing process to bind the perimeter of the case together. This type of construction is particularly useful in the manufacture of eyeglass cases comprising a laminate having a PVC outer layer and an inner layer of soft cushioning material, which layers are sewn together when they are assembled and folded in half longitudinally.
Huber, U.S. Pat. No. 3,819,033, discloses an eyeglass case comprising an inner lining of elastic material surrounded by an outer covering. The edges of the walls are stitched or otherwise secured together. Jacobsen, U.S. Pat. No. 3,559,798, discloses an eyeglass case made from a flexible and stretchable closed cell elastomeric material, which is bonded to an outer skin of stretchable fabric. The folded edges are secured by cementing with glue or adhesive, or by stitching. However, one of the problems associated with the process of Huber or Jacobsen is that the product is inherently weak at the seams and thus not as durable as everyday use requires.
Baratelli, et al., U.S. Pat. No. 4,267,923, disclose an eyeglass case formed by folding a sheet of plastic material longitudinally and securing the edges along two sides by stitching or heat sealing. The case does not have a flock type or other cushioning lining, but consists only of a single layer of a suitable plastic material. Consequently, such a construction provides inadequate protection of the lenses from scratching.
Attempts to introduce a lining layer into the eyeglass case with electronically heat sealed edges were unsuccessful due to the inability of the lining layer to be fused or heat sealed to itself or to the plastic cover. After extensive research and numerous trials the present inventors discovered that by slightly reducing the size of the cushioning liner layer relative to the outer plastic casing material, the plastic sheet could be folded over upon itself with sufficient width of heat sealable plastic around the bottom edge and side wall edges to allow the composite outer casing and cushioning liner to be heat-sealed by fusing the uncovered and contacting edges of the outer plastic layer of heat sealable polyvinyl chloride. However, still further considerable research and experimentation was required in order to develop a process for releasably and uniformly electronically heat-sealing the contacting heat sealable edges without interference by the relatively thick inner cushioning layer.
It is, therefore, an object of this invention to provide an open end type eyeglass case having a heat sealable plastic outer layer bonded to a soft cushioning inner layer in which the edges of the outer layer are electronically heat-sealed to form a reinforced bar tear seal.
It is another object of the present invention to provide a method of manufacturing a thin film open end eyeglass case having a cushioning lining.
More specifically, it is an object of this invention to provide a method of manufacturing a case of the type described using an electronic heat seal to secure the edges along the sides of the case.